The present invention relates to a microwave plasma processing device, and more particularly to a microwave plasma processing device which can stably and efficiently generate plasma when forming a chemical vapor deposition film to a plastic container.
A chemical vapor deposition method (CVD) is a technique which separates out a reaction product in the form of a film on a surface of a processing target by vapor phase epitaxy in a high-temperature atmosphere using a processing gas which causes no reaction at an ordinary temperature, and is widely adopted in manufacture of a semiconductor, surface property modification of a metal or ceramic, and others. In recent years, in the CVD, especially low-pressure plasma CVD has been applied to surface property modification of a plastic container, and an improvement in gas barrier properties in particular.
The plasma CVD performs thin-film growth by utilizing plasma, and it is basically a method which causes in a vapor phase or on a processing target a chemical reaction of a substance generated from dissociation and coupling by discharging a gas containing a processing gas by using an electrical energy of a high electric field under a reduced pressure, thereby depositing the substance on the processing target.
A plasma state is realized by glow discharge, corona discharge and arc discharge and, as types of glow discharge in these discharge schemes, there are known a method utilizing direct-current glow discharge, a method utilizing high-frequency glow discharge, a method utilizing microwave discharge and others.
As an example of forming a vapor disposition carbon film on plastic by utilizing high-frequency glow discharge, there has been disclosed a carbon film coated plastic container having a hard carbon film formed on an inner wall surface of the plastic container.
In the plasma CVD utilizing high-frequency glow discharge, however, since a so-called capacitive coupling type CVD device in which an internal electrode is arranged in a container and an external electrode is arranged outside the container must be used, there is a problem that a configuration of the device becomes complicated and the operation is also complicated.
On the contrary, in microwave plasma CVD, since microwave discharge in a chamber is utilized, the arrangement of an external electrode or an internal electrode is unnecessary, and a configuration of a device can be very simplified. Further, in regard to a level of depressurization in the device, since producing microwave discharge in a plastic container only can suffice, the inside of the entire device does not have to be maintained in a high vacuum state, and this method is superior in the simplicity of the operation and the productivity.
Microwave discharge plasma is plasma which is superior in the efficiency of generation of high-energy electrons, and is useful for the plasma CVD as high-density and high-reactivity plasma.
As a microwave plasma processing method and device aiming at a plastic container, there has been disclosed a method by which a bottle is coaxially arranged in a cylindrical microwave trapping chamber to simultaneously ventilate the inside and outside of the bottle, a processing gas is caused to flow into the bottle for a predetermined processing time, microwaves are introduced into the microwave trapping chamber and plasma is ignited and maintained in the bottle, thereby processing the bottle.
When the microwave plasma processing is utilized, however, since there is a time lag between introduction of microwaves and generation of plasma and this time lag is not fixed and greatly fluctuates in accordance with each processing, there is a drawback that controlling processing conditions is difficult and the effect of processing is unstable.
Furthermore, since the state of plasma is unstable, there is a problem that a container to be processed is locally subjected to thermal deformation or a uniform thin film cannot be formed.
Here, although a method using an electrical spark, a method based on ultraviolet ray irradiation, a method based on a magnetic field operation and others are known as the plasma ignition method, any method has a problem that a configuration of a device becomes complicated.
Moreover, although ignition of plasma can be hastened by increasing an output of a microwave which is introduced into a plasma processing chamber, since processing using plasma with a high energy is carried out from a vapor deposition initial stage when the output of the microwave is increased, an intermediate layer formed between a target substrate to be processed and a vapor deposition film does not sufficiently grow, thereby reducing the adhesion between the target substrate to be processed and the vapor deposition film.
In order to solve the above-described problems, it is an object of the present invention to provide a microwave plasma processing device and a plasma processing gas supply member which can form a uniform thin film on a target substrate to be processed by uniformly forming a processing is gas into plasma with excellent energy efficiency, reduce a time from introduction of a microwave into a plasma processing chamber to plasma emission, and control a timing of ignition of plasma.
Further objects and advantages of the invention will be apparent from the following description of the invention.